We propose to characterize ovarian tumor cell-surface components which are detected by host immunoglobulins, which serve as recognition structures for natural killer cells and which stimulate lymphocytes to produce immunoregulatory factors. We have detected significant amounts of immunoglobulin on the surface of freshly-isolated ovarian tumor cells by immunofluorescence analyses. We have also described an association between the level of a serum IgG complex and the clinical status of ovarian cancer patients. Immunoglobulins have been isolated from both detergent solubilized tumor cells and from the serum IgG complexes obtained from ovarian cancer patients. Preliminary results suggest that these immunoglobulin preparations show significant, reproducible activity for ovarian tumor cells; their specificity, however, remains to be determined. The specificity of these immunoglobulins and characterization of the tumor cell components to which they are directed constitute part of the objectives for the proposed studies. We have also detected significant natural killing (NK) of ovarian tumor cells by normal peripheral blood mononuclear cells. Further, NK can be modulated by cell-free products of mixed lymphocyte-ovarian tumor cell reactions. AN NK enhancing factor similar, if not identical to an interferon has been identified and characterized. We propose to identify ovarian tumor cell-surface components which stimulate production of regulatory products by lymphocytes and those which serve as recognition structures for natural killer cells.